Quality characteristics of soy yogurt produced using proteases and mixed microbial consortia

In this study, we examined the quality characteristics of soy yogurts produced using two proteases(Flavourzyme®and Neutrase®) and the mixed microbial consortia of Lactobacillus bulgaricusand Streptococcus thermophilus(two-mixed) and Lactobacillus acidophilus, Bifidobacterium lactis, and S. thermophilus(three-mixed). The viscosity was the highest in the untreated yogurt. Among the proteolyzed samples, those treated with Flavourzyme®for 20 min showed the highest viscosity, whereas the samples treated with Neutrase®for 30 min and cultured with three-mixed microbial consortia showed the lowest viscosity. The numbers of viable bacteria in the Flavourzyme®-treated samples were slightly greater than those in the Neutrase®-treated samples. The number of viable bacteria increased as hydrolysis time increased. The organic acid content was higher in the three-mixed group than in the two-mixed group, and it was higher in the Flavourzyme®-treated samples than in the Neutrase®-treated samples. Among the Flavourzyme®-treated samples, the three-mixed group showed higher total free amino acid content than the two-mixed group. In contrast, among the Neutrase®-treated samples, those cultured with both mixed microbial consortia produced the similar amounts of free amino acids. The above results showed that proteolytic treatment promoted the growth of lactic acid-producing bacteria. Soy yogurts produced using Flavourzyme®and three-mixed microbial consortia were thought to be more desirable because of more organic acids and free amino acids than those produced using Neutrase®and two-mixed microbial consortia.